天然气水合物沉积物不排水剪切特性的离散元模拟  

DEM simulation on undrained shear characteristics of natural gas hydrate bearing sediments

作　　者：周世琛 郇筱林 陈宇琪 周博[1] 薛世峰[1] 公彬[2,3] Zhou Shichen;Huan Xiaolin;Chen Yuqi;Zhou Bo;Xue Shifeng;Gong Bin(College of Pipeline and Civil Engineering,China University of Petroleum,Shandong Qingdao 266580,China;Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology,Shandong University of Science and Technology,Shandong Qingdao 266590,China;Graduate School of Engineering,Na gasaki University,Nagasaki 852-8521,Japan)

机构地区：[1]中国石油大学(华东)储运与建筑工程学院,山东青岛266580 [2]山东科技大学矿山灾害预防控制省部共建国家重点实验室培育基地,山东青岛266590 [3]长崎大学工学部地盘环境研究室,日本长崎852-8521

出　　处：《石油学报》2021年第1期73-83,共11页Acta Petrolei Sinica

基　　金：国家重点研发计划项目(2017YFC0307604);中国石油大学(华东)研究生创新工程项目(YCX2020071)资助。

摘　　要：天然气水合物资源广泛分布于深海浅层沉积物中,具有储量大、能量密度高、燃烧清洁等优点,是一种极具开发前景的环保能源,深入研究天然气水合物沉积物的力学特性是实现天然气水合物资源安全开采的重要前提。利用常体积方法对天然气水合物沉积物的不排水剪切特性进行了离散元模拟,并依据物理实验结果对数值模拟结果进行了标定,最后对剪切过程中的细观力学机制进行了分析。研究结果表明,离散元模拟能够有效地反映水合物沉积物试样和砂土试样在不排水条件下的宏观力学特性;在剪切过程中,水合物沉积物试样和砂土试样的平均配位数先减小后增加直至达到相对稳定值,而由于水合物的胶结作用,前者配位数的变化幅度较大;接触力链网络初始以环状力链为主,接着以柱状强力链为主,最后以屈曲力链为主;组构异性的演化规律与外部载荷关系密切,接触法向和法向接触力的组构异性的主方向平行于外部荷载方向,而且法向接触力的数值比切向接触力的数值高一个数量级。Natural gas hydrate(NGH), commonly found in deep-sea sediments, has been identified as a promising energy resource due to its abundance in nature, high energy density and clean combustion, and it is crucial for exploring the underlying mechanical properties of natural gas hydrate bearing sediments(NGHBS)for gas recovery. This study aims to investigate the undrained shear behaviors of NGHBS using the discrete element method(DEM). The constant volume method was adopted to simulate the undrained conditions. A series of DEM simulations of biaxial compression tests were performed and then the macromechanical behaviors of NGHBS were presented and verified, and finally mesomechanical mechanisms during shear were examined. The results highlighted that(1)the DEM simulation can effectively reflect the macromechanical properties of NGHBS under undrained conditions;(2)the average mechanical coordination numbers of all samples decrease initially and then increase until it reaches a relatively stable value during shear, and NGHBS samples show greater variances in coordination number compared with sand samples because of the hydrate cementation effect;(3)the force chain network is composed of nearly circular force chains at initial state and then featured by column-like structures and finally consists mostly of buckling force chains;(4)the fabric anisotropy is closely related with the direction of external loading, and the principal directions of fabric anisotropy of contact normals and normal contact forces are parallel with the direction of external loading. Besides, the values of normal contact forces are about an order of magnitude higher than that of the tangential contact forces.

关 键 词：天然气水合物沉积物 不排水条件 宏观力学行为 离散元 细观力学机制 

分 类 号：TE133[石油与天然气工程—油气勘探]